Many car customers of the early 1960's were discovering power steering for the first time. Sure, some cars offered it during the 1950's, but it was a luxury option that was out of reach to the rank and file motorists. Power steering was a new innovation, and I believe the designers were anxious to impress the public over how easy the car is to steer when equipped with this option. So power steering was often "feather-light", even on the heaviest of cars. Fine, except it took a little getting used to, as you had very little "road feel" with this.
In later years the steering assistance was improved, allowing a better feel while still offering power assist. Some cars even have a speed-sensitive arrangement so you have only a little assist when driving, but a lot when parking.
Some of these cars have a similar effect with power brakes. Ever drive a late 60's full-size Mopar? Touch the brakes and they'll be scraping you off the windshield! Again, improved over the years.